Creating Custom Functions
PostgreSQL includes a number of predefined functions to help in data manipulation (see Chapter 4, “PostgreSQL Functions,” for a full listing). Many of the ones included are general-purpose functions that aid in converting, formatting, or aggregating data.
There are many cases in which the system would benefit from the existence of user-defined functions. Functions are particularly useful when the same information needs to be accessed repeatedly. In these cases, it is possible to create a user-defined function that is stored within the server.
Typically, when a function is created, a query plan is precompiled and stored as ready to be executed. This benefits system speed tremendously because the client application only ...
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